The present invention relates to a mine roof support for an underground mine gallery, comprising a sole plate adapted to rest on the floor of a mine gallery and having a front end directed toward the mine face, a rear shield pivotally connected to the other end of the sole plate, while a front shield adapted to engage the roof of a mine gallery is linked to the end of the rear shield which faces the mine face.
In a known mine roof support of the aforementioned kind, the front shield is supported by a prop on the sole plate and fluid operated cylinder and piston means are connected at opposite ends to the front shield and the rear shield, respectively. In such a construction, the free space beneath the front shield which is protected by the latter is relatively small. Due to this disadvantage, such a mine roof support can be used only in mine galleries in which the coal is mined by planing.
In order to increase the free available space beneath the front shield, it is also known to support the rear shield with a prop and to arrange cylinder and piston means between the rear shield and the front shield. In this way a greater free space beneath the front shield will be obtained, so that such mine roof supports may also be used in underground mine galleries in which the coal is mined by rotating cutters. However, in such mine roof supports the danger exists that the front shield will tilt downwardly in an uncontrolled manner if the cylinder and piston means between the front shield and the rear shield should become defective.